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The side-gating effect was demonstrated in AlGaN/GaN heterostructure field effect transistors (HFETs) for the first time. Using 10-µm-thick i-GaN buffer layers, drain currents decreased significantly with the application of a negative bias on a side gate 8 µm away from the FET. The transient responses with LED illumination demonstrated half-recovery condition that can be interpreted as a negative-charge redistribution through a hole emission from traps. The application of a positive side-gate bias confirmed the half-recovery mechanism. From the temperature variation measurements, the trap energy level is estimated to be 0.76 eV from the valence band with a hole capture cross section of approximately 4×10-16 cm2. All these results indicate that the side-gating effect is caused by hole traps in the i-GaN layer, which is in accord with the Shockley–Read–Hall model of deep traps.

A GaN Schottky diode with a lateral structure for microwave power rectification was developed on a semi-insulating silicon carbide substrate. Device evaluation showed that the turn-on voltage was around 0.8 V. The on-resistance of the diode with one finger was 25.6 , the breakdown voltages for those with the field plate reached 93 V, for the wafer with a doping level of 4:0 Â 10 16 cm À3 . The forward and reverse characteristics became stabilized after surface etching. RF measurement at 2.45 GHz showed that the capacitance of the diode was about 0.29 pF at a bias of 0 V. The value is satisfactorily small for microwave rectification. If the superior material characteristics of GaN are fully utilized, GaN Schottky diodes will play key roles in microwave power transmission applications.

Side-gating effects on AlGaN/GaN heterojunction FETs (HFETs) are simulated using a two-dimensional device simulator incorporating the Shockley–Read–Hall (SRH) model for deep traps. With the trap parameters obtained from experiments, the simulation results are in agreement with the experimental results including the “half-recovery” from the side-gating effect and the current reduction in the recovery process from positive side-gate bias application. The simulation indicated that the finite thickness of semi-insulating i-GaN layers suppresses side-gating effects on AlGaN/GaN HFETs with thin i-GaN layers.

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